<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* 交集选择器 */
    div.red {
      color: red
    }

    p.red {
      color: blue;
    }

    /* 并集选择器 */
    div,p{
      font-size: 20px;
    }
  </style>
</head>

<body>
  <div class="red">111111</div>
  <p class="red">22222</p>
  
</body>

</html>